This invention relates generally to a fluid sealing apparatus, and more particularly to a rotary seal.
Radial lip seals are frequently used to provide a fluid seal around a rotating shaft. Typically, these lip seals include an annular outer casing which is secured to the structure surrounding the shaft, and one or more annular seal elements which are held stationary within the outer casing. Each seal element has a cylindrical lip portion which sealingly bears against the shaft. The seal elements also include a radial portion which extends radially outwardly from the lip and which is clamped within the casing so that the seal element remains stationary.
The performance of conventional lip seals under certain operating conditions has been unsatisfactory. Due to the rubbing of the stationary seal element on the rotating shaft, the surface of the shaft which contacts the seal element becomes worn or scored. While shaft scoring can be minimized by using a seal element manufactured from polytetrafluoroethylene and having no abrasive fillers, this often leads to premature seal failure due to rapid wear of the seal element.
Since the lip must always remain in contact with the shaft to form a seal, previous lip seal designs have also been unable to operate satisfactorily when the shaft is significantly misaligned. Likewise, the operation of lip seals is limited in situations where shaft "run-out" or eccentricity is prevalent.
Lip seal performance is also adversely affected by poor or damaged shaft finishes, soft shaft materials, and abrasive fluids. In applications where one or more of the above conditions exist, seal life is often minimal. Since the worn seal element is permanently housed within the casing, the entire seal assembly must be replaced when the seal element is worn. Further, in order to remove the seal assembly, which is generally press-fit into place, the device in which the seal assembly is installed often must be disassembled first.
Thus, a need exists for a rotary seal which is longlasting, easily replaced, and able to perform in adverse operating conditions.